The purpose of this article was to investigate the effect of personal awareness and attitudes, the dentist's role, oral hygiene habits, and fluoride use on total absence of caries in adults, using a case-control study matched for sex and age with undergraduate students from two private Brazilian universities. Crude analysis using conditional logistic regression failed to show any effect for the related variables regarding fluoride use and oral hygiene habits (p > 0.20). Use of dental floss was the only exception in this set. It appeared as a risk factor, since individuals who stated not flossing presented a crude odds ratio (OR) of 0.70, or 0.73 when adjusted for regular visits to the dentist. The effect for regular visits to the dentist was that of a risk. Those with a history of caries presented a crude odds ratio of 1.55; after adjusting for dental floss use, the risk was slightly higher (OR = 1.67). Oral hygiene habits, contrary to the formulated hypothesis, did not display the expected protective effect. Likewise, fluoride use was not significantly associated with absence of caries. Individuals with a history of caries were used to visiting more professionals, confirming the formulated hypothesis for this variable. Nevertheless, it is still intriguing that some people fail to develop caries, even when they report not practicing measures considered ideal for oral health.